Attack database structure

ABSTRACT

Computer program products and methods of inspecting a log of security records in a computer network are provided. The method includes retrieving a log record, processing the log record including deriving a key to a table, determining a data value from information in the log record and adding the data value to a list of data values associated with the key if the data value is unique. One or more entries of the table are evaluated based on predetermined criteria to detect attempted security breaches.

BACKGROUND

[0001] The present invention relates to a method for controllingcomputer network security.

[0002] Firewalls and intrusion detection systems are devices that areused to protect a computer network from unauthorized or disruptiveusers. A firewall can be used to secure a local area network from usersoutside the local area network. A firewall checks, routes, andfrequently labels all messages sent to or from users outside the localarea network. An intrusion detection system (IDS) can be used torecognize suspicious patterns of behavior in a communication system.Examples of an intrusion detection system include a network intrusiondetection system (NIDS) and a host intrusion detection system (HIDS). ANIDS can be used to examine information being communicated within anetwork to recognize suspicious patterns of behavior. A HIDS can be usedto examine information being communicated through a particular hostcomputer within a network to recognize suspicious patterns of behavior.Information obtained by the intrusion detection system (IDS) can be usedto block unauthorized or disruptive users from accessing the network.

[0003] Either a firewall or an intrusion detection system can create logrecords that record incoming and outgoing events into or out of anetwork. Log records can include events such as security violations,bandwidth usage, email usage, and employee access to the Internet.Typically, these log records are reviewed by network securityadministrators in order to detect attempted security breaches or to findtrends in traffic patterns. Since the number of log records is typicallyquite large, query languages are often used to analyze the log recordsto detect attempted security intrusions. Query languages can also beused to analyze the log records and generate reports summarizing theselog records for the network administrator. These reports can be used bythe network administrator to respond to a recognized network securityintrusion. Query language instructions operating on log records can alsobe used to generate alerts for the network administrator. Since thenumber of log records can be quite large, the network security solutionsutilizing query language instructions to analyze the log records can beslow. Query language based solutions can be slow when all the logrecords are analyzed every time a new query is received.

SUMMARY OF THE INVENTION

[0004] The present invention provides a method and apparatus, includingcomputer-program products for detecting attempted network securitybreaches. In one aspect, the invention provides a method of inspecting alog of security records in a computer network and includes retrieving alog record, processing the log record including deriving a key to atable, determining a data value from information in the log record andadding the data value to a list of data values associated with the keyif the data value is unique. The method includes evaluating one or moreentries of the table based on predetermined criteria to detect attemptedsecurity breaches.

[0005] Aspects of the invention can include one or more of the followingfeatures. The table can be a hash table. The list of data values can beimplemented as a linked list. The list of data values can be implementedas a hash table. The list of data values can be implemented as a tree.Evaluating one or more entries of the table can include evaluating allof the entries of the table.

[0006] In another aspect, the invention provides a method of inspectinga log of security records in a computer network and includes retrievinga log record, hashing one or more of the fields of the log record togenerate a hash key, and evaluating a hash table using the hash key. Ifthere is no matching hash table entry, the method includes adding a newentry to the hash table. If there is a matching hash table entry, themethod includes retrieving a data list associated with the hash tableentry and using one or more fields of the log record to compute a datavalue to be inserted into the data list, evaluating the data list todetermine the uniqueness of the data value and inserting the data valuein the data list if the data value is unique.

[0007] In another aspect, the invention provides a method of detecting aport scan and includes retrieving a log record including a sourceaddress and a destination address, hashing the source address and thedestination address to generate a hash key and evaluating a hash tableusing the hash key. If there is a matching hash table entry, the methodincludes retrieving a data list to determine if there are any matchingentries, inserting the destination port with the entries in the datalist if there are no matching entries and determining a port scan if thenumber of items in the data list exceeds a predetermined number.

[0008] In another aspect, the invention includes the computer programproducts for causing a computer to execute instructions to cause dataprocessing apparatus to retrieve a log record, process a log recordincluding deriving a key to a table, determine a data value frominformation in the log record and add the data value to a list of datavalues associated with the key if the data value is unique. One or moreentries of the table are evaluated based on predetermined criteria todetect attempted security breaches.

[0009] Aspects of the invention may include one or more of the followingadvantages. The table may be a hash table. The list of data values maybe implemented as a linked list. The list of data values may beimplemented as a hash table. The list of data values may be implementedas a tree. Instructions to evaluate one or more entries of the table mayinclude instructions to evaluate all the entries of the table.

[0010] In another aspect, the invention includes the computer programproducts for causing a computer to execute instructions to cause dataprocessing apparatus to retrieve a log record, hash one or more fieldsof the log record to generate a hash key, and evaluate a hash tableusing the hash key. If there is no matching hash table entry, theinvention may allow the addition of a new entry to the hash table. Ifthere is a matching hash table entry, the invention may allow retrievalof a data list associated with the hash table entry, use of one or morefields of the log record to compute a data value, comparison of the datavalue with entries in the data list to determine if there are anymatching entries, inserting the data value into the data list if thereare no matching entries, and evaluating the data list based onpredetermined criteria to detect attempted security breaches.

[0011] Aspects of the invention may include one or more of the followingadvantages. The invention may include instructions for adding a newentry to the hash table causing the data processing apparatus togenerate an empty data list associated with the new entry to the hashtable, instructions for inserting a new entry in the data list cause thedata processing apparatus to trigger the evaluation of the data list,instructions for issuing a check table operation causing the dataprocessing apparatus to trigger the evaluation of the data list,instructions for evaluating the data list based on predeterminedcriteria causing the data processing apparatus to block a packetassociated with the log record, instructions for evaluating the datalist based on predetermined criteria causing the data processingapparatus to block all future packets from a same source as a packetassociated with a given log record and instructions for evaluating thedata list based on predetermined criteria causing the data processingapparatus to report an attempted security breach.

[0012] The data list may be a linked list. The data list may be a hashtable. The data list may be a tree. The invention may includeinstructions for evaluating the data list causing the data processingapparatus to evaluate the data list after a plurality of log recordshave been added to the data list. The invention may include instructionsfor evaluating the data list causing the data processing apparatus toevaluate the data list after each log record is added to the data list.The invention may include instructions for evaluating the hash tableusing the hash key causing the data processing apparatus to process asecond hash table. The invention may include instructions for processinga second hash table causing the data processing apparatus to use thematching hash table entry to retrieve a second hash table, and using thehash key to evaluate the second hash table. If there is no matchingsecond hash table entry, the invention may allow the addition of a newentry to the second hash table. If there is a matching second hash tableentry, the invention may allow retrieval of a second data listassociated with the second hash table entry, comparing the data valuewith entries in the second data list to determine if there are anymatching entries, inserting the data value in the second data list ifthere are no matching entries and evaluating the second data list basedon predetermined criteria to detect attempted security breaches.

[0013] In another aspect, the invention, embodied in an informationcarrier for inspecting a log of security records in a computer networkincludes a computer program product for causing the computer to executeinstructions to cause the data processing apparatus to retrieve a logrecord, hash one or more fields of the log record to generate a hash keyand evaluate a hash table using the hash key. If there is no matchinghash table entry, the invention allows adding a new entry to the hashtable. If there is a matching hash table entry, the invention allowsretrieving a data list associated with the hash table entry, using oneor more fields of the log record to compute a data value to be insertedinto the data list, evaluating the data list to determine the uniquenessof the data value and inserting the data value in the data list if thedata value is unique.

[0014] In another aspect, the invention, embodied in an informationcarrier for detecting a port scan, includes a computer program productfor causing a computer to execute instructions to cause the dataprocessing apparatus to retrieve a log record including a source addressand a destination address, hash the source address and the destinationaddress to generate a hash key, and evaluate a hash table using the hashkey. If there is a matching hash table entry, the invention allowsretrieving a data list associated with the hash table entry, comparingthe destination port with the entries in the data list to determine ifthere are any matching entries, inserting the destination port into thedata list if there are no matching entries and determining a port scanif the number of items in the data list exceeds a predetermined number.

[0015] Advantages of the invention may include one or more of thefollowing features. Each log record needs to be processed only once whenit is first received. The analysis of log records can be fast because ahash table is used to store and retrieve the log records. Storing theprocessed log records instead of the log record itself can require lessmemory capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1A shows a network topology including a NIDS operating ininline mode.

[0017]FIG. 1B shows a network topology including a NIDS operating innon-inline mode.

[0018]FIG. 2 is a flowchart describing the operation of a recordprocessing unit.

[0019]FIG. 3 is a flowchart for building a table in static mode.

[0020]FIG. 4 is a flowchart for building a table in dynamic mode.

[0021]FIG. 5 describes a table data structure.

[0022]FIG. 6 is a flowchart for creating a table data structure.

[0023]FIG. 7 is a flowchart for evaluating the table data structure.

[0024]FIG. 8 illustrates the use of multiple hash tables.

[0025]FIG. 9 illustrates the use of cascaded hash tables.

[0026]FIG. 10 shows a method for detecting a port scan attack.

[0027] Like reference numbers and designations in the various drawingsindicate like elements.

DETAILED DESCRIPTION

[0028]FIG. 1A shows a network topology including a local area network(LAN) 100, including a server 102, several workstations (W/S) 104, afirewall 106, and NIDS 108. The NIDS 108 operates in inline mode andanalyzes information as it is being communicated in the network. The LAN100 is connected to an external network, e.g., the Internet 114, throughthe firewall 106. The LAN 100 is also connected to a second LAN 116through a router 118, and satellite 120. Second LAN 116 includes a webserver 110, an email server 112, a server 102, several workstations 104,a firewall 106 and NIDS 108. The computers, servers and other devices inthe LAN are interconnected using a number of data transmission mediasuch as wire, fiber optics, and radio waves. Each LAN uses intrusiondetection systems to analyze messages being communicated within thenetwork and recognize suspicious patterns of behavior. Each LAN 100 and116 includes a record processing unit 122 connected to firewall 106 andNIDS 108. The record processing unit (RPU) 122 receives log records fromone of firewall 106 and NIDS 108 and analyzes the log records to detectattempted network security intrusions. Alternatively, the NIDS can beconfigured outside the transmission path, in a passive (non-inline)mode. In the non-inline mode, the NIDS device monitors and inspectstraffic received by the network, but only reports (i.e., does not droppackets) that are determined to match specified attack signatures. FIG.1B shows a network topology including NIDS 124 operating in non-inlinemode. The NIDS 124 receives information being communicated in thenetwork, determines attacks and can report or otherwise passively act toblock future communications from unauthorized or disruptive users.

[0029]FIG. 2 is a block diagram of the RPU 122. The RPU 122 includes aninterface 202 for communicating (e.g. to firewalls, and intrusiondetection systems) with one or more security devices on the network.Interface 202 is used to receive security logs. The RPU 122 uses aprocessing engine 204 to process security logs received from thesecurity devices on the network. The processed log records are stored ina database 208. An evaluation engine 206 uses the processed log recordsstored in the database 208 to detect attempted network securitybreaches. Any attempted network security breaches detected by RPU 122can be communicated to a respective security device using interface 202.

[0030] RPU 122 can be operated in at least two different modes. In thefirst mode, a plurality of log records are received and processed. Thefirst mode is referred to as the off-line mode. In the second mode, theRPU receives and processes individual log records as they are generated.The second mode is referred to as the on-line mode.

[0031]FIG. 3 is a flow diagram describing the off-line mode ofoperation. In the off-line mode, a log of records is communicated to theRPU 122. The log can be produced by security devices on the networkbased on incoming or outgoing communications. The RPU 122 receives thelog records (step 300) and retrieves individual records (step 302) forprocessing. The log record is used to build and update a table datastructure (step 304). If there are additional log records that need tobe processed (step 306) control passes to step 302 at which time theprocess repeats and the next log record is processed. In oneimplementation, the table data structure is evaluated (step 308) afterall the log entries have been processed and RPU 122 responds if anyattempted security intrusion is detected (step 310). In response to anattempted security intrusion, the RPU 122 can communicate the attemptedsecurity intrusion to the security device (e.g. firewall, IDS) or otherdevices on the network. In one implementation, RPU 122 can block allfuture packets from the source responsible for the attempted intrusion(e.g., by communicating a rule to the firewall to block all packets fromthe responsible source). RPU 122 can also report the attempted securityintrusion to the administrator for an appropriate response.

[0032]FIG. 4 is a flow diagram describing the on-line mode of operation.In the on-line mode, individual log records are received by RPU 122 forprocessing (step 400). In the on-line mode, RPU 122 processes individuallog records as they are received. The processed log records are used toupdate the table data structure (402) and the resulting table datastructure is evaluated (404) after each log record is processed.Thereafter, RPU 122 responds to any attempted intrusion (406) before RPU122 starts processing the next log record.

[0033]FIG. 5 describes one example of a table data structure used by RPU122. Referring now to FIGS. 2 and 5, a hash key 512 generated by theprocessing engine 204 from the fields of the log record, is used togenerate an address for an entry in the hash table 500 using a tableaddress generator 508. The address generated by the table addressgenerator 508 is used to look up the selected entry in hash table 500.Each hash table entry can either be a data value 502, a list of datavalues 504, a pointer to a data value or a data list 506. Entries thatconsist of a data value or a set of data values (502 or 506) can bestored directly in the hash table 500 in database 208. For data lists,the hash table entry can be a pointer to the data list 506 in database208. The data list 510 contains a list of data values and can beimplemented using a linked list or any other suitable data structure.

[0034] The data entries in hash table 500 and the data list 510 can betagged to expire after a predetermined duration of time. A timer 509 canbe used by the processing engine to measure a specific duration time fora given data entry stored in the hash table or data list. The data entrycan be deleted when the time duration has expired. One simple timerimplementation includes the tagging of each entry with a time stamp. Atevaluation time, the current time can be compared to the stamped time.Entries that are too old can be removed prior to the evaluation step.

[0035]FIG. 6 is a flow diagram depicting the creation of the table datastructure. RPU 122 (FIG. 1a) receives one or more logs (step 600) fromone or more security devices on the network. Individual log records areretrieved (step 602) and the fields of the log record are used togenerate a hash key (step 604). The generated hash key is used toevaluate a hash table (step 606). If a matching entry is found in thehash table (step 608) a data list associated with the selected hashtable entry (step 610) is retrieved. A data value generated using one ormore fields of the log record (step 624), is compared with the datavalues in the data list (step 612). Only unique data values are insertedinto the data list. If a matching entry is found in the data list (step614), the data value derived from the log record is not inserted intothe data list (step 616). If no matching entry is found in the datalist, the data value is inserted into the data list (step 618) andcontrol passes to step 602 at which time the process repeats and thenext log record is processed. If no matching entry is found in the hashtable during step 608, a new hash table entry and a new data list arecreated (step 620). The new data list is associated (step 622) with thehash table entry indicated by the generated hash key and the data valuegenerated using the fields of the log record (step 624) is inserted intothe data list (step 618). Following the completion of step 618 controlpasses to step 602 at which time the process repeats for each log recordreceived.

[0036]FIG. 7 is a flow diagram describing a process of evaluating a hashtable to detect attempted security breaches. The table data structurecan be evaluated whenever a new entry is added to a hash table or to adata list that is part of the table data structure. In addition, a“Check Table” operation, initiated by a user, can also trigger anevaluation of the table data structure. In one implementation, the tabledata structure is evaluated by retrieving each hash table entry (step700). If the entry is a pointer to a data list (step 702) the data listis retrieved (step 704). If the table entry contains a data value or aset of data values these values are retrieved (step 706). The datavalues retrieved in step 704 or step 706 are compared againstpredetermined criteria to determine if there has been an attemptedsecurity breach (step 708). If an attempted intrusion is detected, RPU122 can take one of a plurality of actions based on the nature of theattempted breach (step 710). RPU 122 can communicate with the NIDS orfirewall to drop the current packet associated with the log record. RPU122 can also block all future packets originating from the same sourcein response to an attempted security breach. In addition, RPU 122 canreport any attempted security breach to the administrator forappropriate response. This process is repeated for all the entries inthe hash table.

[0037] In an alternative implementation of the hash table evaluationprocess, only table entries that have been modified after the previoustable evaluation are considered during the evaluation process. This canbe accomplished by including tag fields in the hash table entry toindicate any entries that are modified as a result of inserting a newdata value in the table data structure. The tag field is used to locatemodified data values during the table evaluation process. The tag fieldscan be reset after the modified data has been used to evaluate thetable. In another implementation of the hash table evaluation process,the hash table is evaluated immediately after inserting a new data valuein the table data structure (i.e., right after step 618 above in FIG.6).

[0038] RPU 122 can employ more than one hash table. FIG. 8 illustratesan example using more than one hash table to detect an attemptedsecurity intrusion. In the example, a log record is obtained by RPU 122during either the on-line or off-line mode of operation (step 800). Anevaluation strategy is determined using the log record, a hash keygenerated from the log record, or a combination of the log record and ahash key derived from the log record (step 805). The evaluation strategycan be used to identify the number of tests and the type of tests thatshould be performed for the given record. The evaluation strategy can bebased on a number of criteria including, known attack signatures andprior log records originating from the same source. A number of hashkeys are generated, based on the evaluation strategy, for the differenttype of tests that must be performed (step 815). The generated hash keysare used to update the hash tables associated with the tests to beperformed (step 820). The hash tables associated with the tests areevaluated to determine if there has been an attempted security intrusion(step 825). In this example, all the hash keys and all the hash tablesmay not be distinct. It is possible to use the same hash key to updateand evaluate two different hash tables. It is also possible to use twodifferent hash keys to evaluate the same hash table as part of twodifferent tests.

[0039]FIG. 9 illustrates an example using cascaded hash tables to detectan attempted security intrusion. In this example, as part of the tableevaluation process, a first hash table entry is retrieved from a firsthash table. The first hash table entry is checked by comparing the firsthash table entry against a predetermined criteria (step 900). Theevaluation process for detecting a particular security intrusion mayrequire the evaluation of a second hash table. A second hash key for thesecond hash table can be generated using the first hash key, the firsthash table entry selected by the first hash key, or a combination of thefirst hash key and the first hash table entry selected by the first hashkey (step 905). The second hash table is updated using the second hashkey (step 910) and the second hash table is evaluated to determine ifthere has been an attempted security intrusion (step 915). Theevaluation of the individual hash tables is as described above withrespect to FIG. 6.

[0040]FIG. 10 shows an exemplary method for detecting a port scanningattack. Port scanning, a frequently used approach for attacking computersecurity, gives a hacker an idea where to look for weaknesses. A portscan comprises a series of messages sent by the hacker attempting toprobe a computer to learn which computer network services, eachassociated with a “well-known” port number, the computer provides.Essentially, the port scan consists of sending a message to each port,e.g., one at a time. The kind of response received indicates whether theport is used and accessible and can therefore be probed for weaknesses.In the present example, a log of records that include port queries isevaluated. The log can be generated by a router, firewall or othersecurity device. RPU 122 extracts the source and destination IPaddresses from the log records received (step 1000). The source anddestination IP addresses as reported by the log record are used togenerate a hash key (step 1005). The generated hash key is used by atable address generator 1010 to evaluate a first hash table 1015. RPU122 adds any unique port numbers accessed by the application to the datalist 1025 indicated by the hash table entry 1020 selected by thegenerated hash key. During a typical port scan attack, the data list1025 accumulates a large number of entries as the hacker attempts toaccess a large number of ports within a short time interval. Each portnumber added to the data list 1025 can be tagged to expire after apredetermined duration of time, for example, using the timer 509 (FIG.5). Once the data list 1025 accumulates a predetermined number ofentries, a port scan is detected. The source and destination IPaddresses included in the hash key can be used to determine the sourceof the scan and the computer that is being scanned.

[0041] In another example, the techniques disclosed can be used todetect a mail server attack. A typical mail server attack can proceed inthree phases. During the first phase of the attack, a hacker can attemptto connect to a mail server running on a well-known port number (e.g.,most SMTP mail servers run on port 25) A first entry can be stored inthe database (e.g., hash table) associated with this first phase of theattack. More particularly, a hash key derived from the source addressassociated with the potential hacker can be used to point to a record inthe hash table. At the time of the first attack, the record can bepopulated with a first entry indicating that a potential hacker from theidentified source address has contacted the mail server. During thesecond phase of the attack, a NIDS or a HIDS detects a exploitationattempt, e.g., a buffer overflow. The exploitation attempt is associatedwith a particular source, and accordingly, a check can be made in thehash table for a record associated with the source. More specifically,the source address is used to generate a key, which then is used to scanthe hash table for a. matching entry. If matching record is located inthe database, then a second element can be added to the located recordto indicate that the source attempted a detected exploitation of thesystem. During the third phase of the attack, the mail server caninitiate a connection to the network, as the hacker controls the mailserver and successfully uses the mail server to send the hackerprotected information (e.g., a password file). If an attempt to gaincontrol of the mail server is detected, once again, the hash table canbe updated. More specifically, a key is derived from the address of thehacker that has been detected as attempting to take over the mailserver. The key is used to locate the appropriate record in the hashtable associated with the hacker. The third phase can result in thepopulation of a third element in the record associated with the hacker,indicative of the attempted take over of the mail server. At a time forevaluation, the sequence of attack events (port scan, exploitation, andmail server take over) can be recognized as a mail server attack and anappropriate response generated.

[0042] The invention can be implemented in digital electronic circuitry,or in computer hardware, firmware, software, or in combinations of them.The invention can be implemented as a computer program product, i.e., acomputer program tangibly embodied in an information carrier, e.g., in amachine-readable storage device or in a propagated signal, for executionby, or to control the operation of, data processing apparatus, e.g., aprogrammable processor, a computer, or multiple computers. A computerprogram can be written in any form of programming language, includingcompiled or interpreted languages, and it can be deployed in any form,including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a communication network.

[0043] Method steps of the invention can be performed by one or moreprogrammable processors executing a computer program to performfunctions of the invention by operating on input data and generatingoutput. Method steps can also be performed by, and apparatus of theinvention can be implemented as, special purpose logic circuitry, e.g.,an FPGA (field programmable gate array) or an ASIC (application-specificintegrated circuit).

[0044] Processors suitable for the execution of a computer programinclude, by way of example, both general and special purposemicroprocessors, and any one or more processors of any kind of digitalcomputer. Generally, a processor will receive instructions and data froma read-only memory or a random access memory or both. The essentialelements of a computer are a processor for executing instructions andone or more memory devices for storing instructions and data. Generally,a computer will also include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, e.g., magnetic, magneto-optical disks, or optical disks.Information carriers suitable for embodying computer programinstructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, e.g., EPROM,EEPROM, and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The processor and the memory can be supplemented by, orincorporated in special purpose logic circuitry.

[0045] The invention can be implemented in a computing system thatincludes a back-end component, e.g., as a data server, or that includesa middleware component, e.g., an application server, or that includes afront-end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user can interact with animplementation of the invention, or any combination of such back-end,middleware, or front-end components. The components of the system can beinterconnected by any form or medium of digital data communication,e.g., a communication network. Examples of communication networksinclude a local area network (“LAN”) and a wide area network (“WAN”),e.g., the Internet.

[0046] The computing system can include clients and servers. A clientand server are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

[0047] This invention has been described in terms of particularembodiments. Nevertheless, it will be understood that variousmodifications may be made without departing from the spirit and scope ofthe invention. For instance, the steps of the invention can be performedin a different order and still achieve desirable results. Instead ofusing hash tables, other equivalent data structures can be used. Thehash tables can be stored using an SQL database. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A method of inspecting a log of security recordsin a computer network, comprising the steps of: retrieving a log record;processing the log record including deriving a key to a table;determining a data value from information in the log record and addingthe data value to a list of data values associated with the key if thedata value is unique; and evaluating one or more entries of the tablebased on predetermined criteria to detect attempted security breaches.2. The method of claim 1, wherein the table is a hash table.
 3. Themethod of claim 1, wherein the list of data values is implemented as alinked list.
 4. The method of claim 1, wherein the list of data valuesis implemented as a hash table.
 5. The method of claim 1, wherein thelist of data values is implemented as a tree.
 6. The method of claim 1,wherein evaluating one or more entries of the table includes evaluatingall the entries of the table.
 7. A method of inspecting a log ofsecurity records in a computer network, comprising the steps of:retrieving a log record; hashing one or more fields of the log record togenerate a hash key; evaluating a hash table using the hash key; ifthere is no matching hash table entry, adding a new entry to the hashtable; if there is a matching hash table entry, retrieving a data listassociated with the hash table entry; using one or more fields of thelog record to compute a data value; comparing the data value withentries in the data list to determine if there are any matching entries;inserting the data value into the data list if there are no matchingentries; and evaluating the data list based on predetermined criteria todetect attempted security breaches.
 8. The method of claim 7, whereinadding a new entry to the hash table includes generating an empty datalist associated with the new entry to the hash table.
 9. The method ofclaim 7, wherein inserting a new entry in the data list includestriggering an evaluation of the data list.
 10. The method of claim 7,including receiving a check table operation to trigger the evaluation ofthe data list.
 11. The method of claim 7, wherein evaluating the datalist based on predetermined criteria includes blocking a packetassociated with the log record.
 12. The method of claim 7, whereinevaluating the data list based on predetermined criteria includesblocking all future packets from a same source as a packet associatedwith a given log record.
 13. The method of claim 7, wherein evaluatingthe data list based on predetermined criteria includes reporting anattempted security breach.
 14. The method of claim 7, wherein the datalist is a linked list.
 15. The method of claim 7, wherein the data listis a hash table.
 16. The method of claim 7, wherein the data list is atree.
 17. The method of claim 7, including evaluating the data listafter a plurality of log records have been added to the data list. 18.The method of claim 7, including evaluating the data list after each logrecord is added to the data list.
 19. The method of claim 7, whereinevaluating the hash table using the hash key includes processing asecond hash table.
 20. The method of claim 19, wherein processing asecond hash table includes: using the matching hash table entry toretrieve a second hash table; using the hash key to evaluate the secondhash table; if there is no matching second hash table entry, adding anew entry to the second hash table; if there is a matching second hashtable entry, retrieving a second data list associated with the secondhash table entry; comparing the data value with entries in the seconddata list to determine if there are any matching entries; inserting thedata value in the second data list if there are no matching entries; andevaluating the second data list based on predetermined criteria todetect attempted security breaches.
 21. A method of inspecting a log ofsecurity records in a computer network, comprising the steps of:retrieving a log record; hashing one or more fields of the log record togenerate a hash key; evaluating a hash table using the hash key; ifthere is no matching hash table entry, adding a new entry to the hashtable; if there is a matching hash table entry, retrieving a data listassociated with the hash table entry; using one or more fields of thelog record to compute a data value to be inserted into the data list;evaluating the data list to determine the uniqueness of the data value;and inserting the data value in the data list if the data value isunique.
 22. A method of detecting a port scan comprising: retrieving alog record including a source address and a destination address; hashingthe source address and the destination address to generate a hash key;evaluating a hash table using the hash key; if there is a matching hashtable entry, retrieving a data list associated with the hash tableentry; comparing the destination port with the entries in the data listto determine if there are any matching entries; inserting thedestination port into the data list if there are no matching entries;and determining a port scan if the number of items in the data listexceeds a predetermined number.
 23. A computer program product, tangiblyembodied in an information carrier, the computer program productcomprising instructions operable to cause data processing apparatus to:retrieve a log record; process a log record including deriving a key toa table; determine a data value from information in the log record andadding the data value to a list of data values associated with the keyif the data value is unique; and evaluate one or more entries of thetable based on predetermined criteria to detect attempted securitybreaches.
 24. The computer program product of claim 23, wherein thetable is a hash table.
 25. The computer program product of claim 23,wherein the list of data values is implemented as a linked list.
 26. Thecomputer program product of claim 23, wherein the list of data values isimplemented as a hash table.
 27. The computer program product of claim23, wherein the list of data values is implemented as a tree.
 28. Thecomputer program product of claim 23, wherein instructions to evaluateone or more entries of the table include instructions to evaluate allthe entries of the table.
 29. A computer program product, tangiblyembodied in an information carrier, the computer program productcomprising instructions operable to cause data processing apparatus to:retrieve a log record; hash one or more fields of the log record togenerate a hash key; evaluate a hash table using the hash key; if thereis no matching hash table entry, add a new entry to the hash table; ifthere is a matching hash table entry, retrieve a data list associatedwith the hash table entry; use one or more fields of the log record tocompute a data value; compare the data value with entries in the datalist to determine if there are any matching entries; insert the datavalue into the data list if there are no matching entries; and evaluatethe data list based on predetermined criteria to detect attemptedsecurity breaches.
 30. The computer program product of claim 29, whereininstructions for adding a new entry to the hash table cause the dataprocessing apparatus to generate an empty data list associated with thenew entry to the hash table.
 31. The computer program product of claim29, wherein instructions for inserting a new entry in the data listcause the data processing apparatus to trigger the evaluation of thedata list.
 32. The computer program product of claim 29, whereininstructions for issuing a check table operation cause the dataprocessing apparatus to trigger the evaluation of the data list.
 33. Thecomputer program product of claim 29, wherein instructions forevaluating the data list based on predetermined criteria cause the dataprocessing apparatus to block a packet associated with the log record.34. The computer program product of claim 29, wherein instructions forevaluating the data list based on predetermined criteria cause the dataprocessing apparatus to block all future packets from a same source as apacket associated with a given log record.
 35. The computer programproduct of claim 29, wherein instructions for evaluating the data listbased on predetermined criteria cause the data processing apparatus toreport an attempted security breach.
 36. The computer program product ofclaim 29, wherein the data list is a linked list.
 37. The computerprogram product of claim 29, wherein the data list is a hash table. 38.The computer program product of claim 29, wherein the data list is atree
 39. The computer program product of claim 29, wherein instructionsfor evaluating the data list cause the data processing apparatus toevaluate the data list after a plurality of log records have been addedto the data list.
 40. The computer program product of claim 29, whereininstructions for evaluating the data list cause the data processingapparatus to evaluate the data list after each log record is added tothe data list.
 41. The computer program product of claim 29, whereininstructions for evaluating the hash table using the hash key cause thedata processing apparatus to process a second hash table.
 42. Thecomputer program product of claim 41, wherein instructions forprocessing a second hash table cause the data processing apparatus to:use the matching hash table entry to retrieve a second hash table; usethe hash key to evaluate the second hash table; if there is no matchingsecond hash table entry, add a new entry to the second hash table; ifthere is a matching second hash table entry, retrieve a second data listassociated with the second hash table entry; compare the data value withentries in the second data list to determine if there are any matchingentries; insert the data value in the second data list if there are nomatching entries; and evaluate the second data list based onpredetermined criteria to detect attempted security breaches.
 43. Acomputer program product, tangibly embodied in an information carrier,for inspecting a log of security records in a computer network, thecomputer program product comprising instructions operable to cause dataprocessing apparatus to: retrieve a log record; hash one or more fieldsof the log record to generate a hash key; evaluate a hash table usingthe hash key; if there is no matching hash table entry, add a new entryto the hash table; if there is a matching hash table entry, retrieve adata list associated with the hash table entry; use one or more fieldsof the log record to compute a data value to be inserted into the datalist; evaluate the data list to determine the uniqueness of the datavalue; and insert the data value in the data list if the data value isunique.
 44. A computer program product, tangibly embodied in aninformation carrier, for detecting a port scan, the computer programproduct comprising instructions operable to cause data processingapparatus to: retrieve a log record including a source address and adestination address; hash the source address and the destination addressto generate a hash key; evaluate a hash table using the hash key; ifthere is a matching hash table entry, retrieve a data list associatedwith the hash table entry; compare the destination port with the entriesin the data list to determine if there are any matching entries; insertthe destination port into the data list if there are no matchingentries; and determine a port scan if the number of items in the datalist exceeds a predetermined number.